A capacitance type semiconductor physical quantity sensor includes a movable electrode and a fixed electrode located opposite to the movable electrode, which are formed on a support substrate. A physical quantity is detected based upon a capacitance change between the movable electrode and the fixed electrode.
Generally speaking, this sort of semiconductor physical quantity sensor is equipped with a movable electrode and a fixed electrode, and detects a physical quantity based upon a capacitance change between the movable electrode and the fixed electrode when a physical quantity is applied to this sensor. The movable electrode is coupled on a support substrate under such a condition that the movable electrode is movable with respect to the support substrate. The fixed electrode is coupled on the support substrate under such a condition that the fixed electrode is fixed to the support substrate, and arranged opposite to the movable electrode.
As such a semiconductor physical quantity sensor for measuring a physical quantity based upon a change in an electrostatic capacitance, acceleration sensors, angular rate sensors, gyroscopes, pressure sensors, and the like are known in this field.
Then, these capacitance type semiconductor physical quantity sensors are applied to various sorts of utilizations as, for example, sensors for controlling automobile-purpose air bags, sensors for controlling stabilities of automotive vehicles, and sensors for commercial-purpose game amusements, and the like.
Such semiconductor physical quantity sensors can be manufactured in accordance with a manufacturing method to which a semiconductor technique is applied, namely, such a manufacturing method utilizing a so-called “MEMS (Micro Electro Mechanical Systems).” This general-purpose manufacturing method is carried out as follows:
First, a stacked layer substrate is prepared which is manufactured by stacking semiconductor layers via an insulating layer on a support substrate. As such a stacked layer substrate, a silicon-on insulator substrate (SOI substrate) is typically employed in which both a support substrate and a semiconductor layer are made of silicon, and an insulating layer is made of a silicon oxide film.
Then, trenches are formed with respect to the semiconductor layer of the stacked layer substrate, while the trenches are reached from a front surface of the semiconductor layer to the insulating layer, and segment patterns of a movable electrode and a fixed electrode. Thereafter, such an insulating layer is removed which is positioned under a sensor portion which should constitute the movable electrode in order that the movable electrode is released from the support substrate. As a result, a semiconductor physical quantity sensor is manufactured.
In this case, in this sort of semiconductor physical quantity sensor, as to electrode materials of a movable electrode and a fixed electrode which are employed so as to provide capacitances, low-cost single crystal silicon and polycrystal silicon is employed as semiconductor materials in order to employ semiconductor techniques.
More specifically, in order to improve sensor sensitivities, it is preferable to form a single crystal silicon electrode by employing an adhered SOI wafer for the sake of an increase of a capacitance value between a movable electrode and a fixed electrode. In this adhered SOI wafer, thicknesses of these electrodes can be readily achieved.
Also, in the MEMS technique, a desirable structural body is formed by using both a front surface processing operation and a rear surface processing operation of a semiconductor silicon wafer. Due to a matching characteristic with respect to a general-purpose LSI manufacturing facility, if this semiconductor silicon wafer can be processed from the front surface thereof, then a more convenient effect may be achieved.
For instance, as a conventional method for manufacturing this sort of the semiconductor physical quantity sensor, one method of forming a semiconductor physical quantity sensor in which an SOI substrate is employed and an embedded oxide film corresponding to an insulating layer is employed as a sacrifice layer is proposed. This method is disclosed in, for example, Japanese Laid-open Patent Application No. Hei-6-349806, which corresponds to U.S. Pat. No. 5,616,523.
On the other hand, typical layer thickness is a smaller dimension than 1 micrometer. Therefore, the dimension of the gap among the movable electrode and the fixed electrode and also the support substrate which corresponds to the supporting member of these electrodes is secured by the thickness of the thin embedded oxide film.
Here, thicknesses of embedded oxide films of SOI wafers are nearly equal to several micrometers (2 to 3 micrometers) at the most. Accordingly, the gap between the movable electrode and the fixed electrode is as thin as several microns at the most.
However, in such a case that semiconductor physical quantity sensors having such a thin gap between these electrodes and the support substrates are manufactured, there are some possibilities that foreign matters such as particles are mixed in this gap in the manufacturing stage thereof.
If the mixtures of these foreign matters occur, then the movable electrode which should be released via the above-described gap on the support substrate may abut against these foreign matters, and thus, can be hardly moved. Thus, the normal movement of the movable electrode is impeded. As previously explained, the mixture of the foreign matters may conduct problems in sensor characteristics, and also, may lower the field of the production.
In this case, the below-mentioned method using such an SOI wafer is conceivable. That is, in this SOI wafer, even when foreign matters are mixed into the air gap between the movable electrode and the support substrate, the thickness of the sacrifice layer is made thicker, namely the thickness of the embedded oxide film corresponding to the insulating layer is made thicker in order to suppress the adverse influence caused by these foreign matters.
As a result of this method using such an SOI wafer, it is conceivable that since the gap may be widened, the interference between the movable electrode and the foreign matters can be suppressed. However, generally speaking, since the SOI wafers having the thick thicknesses of the embedded oxide films as the sacrifice layers become high cost, the use of these SOI wafers is not desirable. Thus, it is required to improve a production yield caused by mixtures of foreign matters between the movable electrode and the support substrate, while a thickness of an insulating layer corresponding to a sacrifice layer is not made thick.